1. Field of the Invention
This invention relates generally to the field of x-ray diffraction and, more particularly, to x-ray detectors that use readout strips for the detection of electrons generated by incoming x-ray energy.
2. Description of the Related Art
In the field of x-ray diffraction, particularly small-angle x-ray scattering (SAXS), a sample is subjected an incident x-ray beam, and a low-angle x-ray diffraction signal from the sample is recorded with a detector. A typical SAXS configuration, known as a Kratky camera, is shown schematically in FIG. 1. In this configuration, an x-ray beam 10 from an x-ray source (not shown) is directed toward offset blocks 12 and 14 that, together, make up a Kratky collimator. The Kratky collimator shapes the beam to a ribbon-like profile, having a long, thin cross section. Due to the arrangement of the blocks 12, 14, there is very little scattering of the x-ray beam, and thus minimal background noise, to the side of the beam on which the block 14 is located. In the path of the collimated beam is located a sample 16 that, in this example, is a liquid in a capillary tube. Small-angle scatter from the sample 16 is then collected by a detector 18, which may be either a one-dimensional or a two-dimensional detector. As shown in the figure, the detector is positioned such that the distribution of the diffraction signal is centered along the edge of the detector, so that the detection surface resides in the region of minimal x-ray scatter (i.e., to the same side of the beam as collimator block 14). As such, only a portion (typically half) of the diffraction signal from the sample 16 is collected.
Because the distribution of x-rays is isotropic, a one-dimensional detector is often used to record the scattered radial x-ray profile. One-dimensional detectors (also known as linear or “strip” detectors) have the advantage of being simpler, less expensive and less complex than two-dimensional detectors. One type of linear detector makes use of a series of straight readout strips as shown schematically in the example of FIG. 2. The detector 20 may be based on a gas electron multiplier, or it may be a semiconductor detector, and it includes readout strips 22 that run parallel to one another, covering an area upon which the diffraction signal is incident (indicated at 24 in the figure). The strips may consist of, for example, silicon diodes in a semiconductor strip detector, or metallic strips in a gaseous detector.
In the example of FIG. 2, each of the readout strips detects photoelectrons generated from the interaction of the x-ray energy with a gas or a semiconductor material. There is no spatial discrimination in a direction parallel to the strips, and the accumulated electron signal for the entire strip must be read out together. Typically, the readout strips are connected to a delay line that is, in turn, connected to a time-to-digital converter to record the x-ray positional data. Alternatively, each strip may be connected a preamplifier which is connected to multichannel readout electronics.